Cage Fleece

I just lay it loose on top of wood pellets. You need fleece on top of an absorbent layer, so there is something between the fleece and the coroplast floor. It moves around a bit but not much.
If your guinea pigs burrow under the fleece you can carry it up and over the edged of the coroplast.

You can also use fleece pads - a layer of towel or uhal pad covered in fleece. You can buy them or sew them yourself.

I currently have fleece over wood pellets. I like the look of having the fleece over the coroplast and just tuck it under. I've used a wide range of things in the past. Initially I cut a piece of coroplast that fit inside my liner and then cut a uhaul pad the same size. I would cover the uhaul pad with fleece, tuck it under and then hold it together with binder clips ( I did this to make it easier to sweep). I've also used fleece pads that I made that just laid in the cage. I've also tucked the edged of the fleece under my absorbant layer to make the edges look clean.